// SPDX-License-Identifier: GPL-2.0

#include <linux/errno.h>

int ceph_armor(char *dst, const char *src, const char *end);
int ceph_unarmor(char *dst, const char *src, const char *end);

/*
 * base64 encode/decode.
 */

static const char *pem_key =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static int encode_bits(int c)
{
        return pem_key[c];
}

static int decode_bits(char c)
{
        if (c >= 'A' && c <= 'Z')
                return c - 'A';
        if (c >= 'a' && c <= 'z')
                return c - 'a' + 26;
        if (c >= '0' && c <= '9')
                return c - '0' + 52;
        if (c == '+')
                return 62;
        if (c == '/')
                return 63;
        if (c == '=')
                return 0; /* just non-negative, please */
        return -EINVAL;
}

int ceph_armor(char *dst, const char *src, const char *end)
{
        int olen = 0;
        int line = 0;

        while (src < end) {
                unsigned char a, b, c;

                a = *src++;
                *dst++ = encode_bits(a >> 2);
                if (src < end) {
                        b = *src++;
                        *dst++ = encode_bits(((a & 3) << 4) | (b >> 4));
                        if (src < end) {
                                c = *src++;
                                *dst++ = encode_bits(((b & 15) << 2) |
                                                     (c >> 6));
                                *dst++ = encode_bits(c & 63);
                        } else {
                                *dst++ = encode_bits((b & 15) << 2);
                                *dst++ = '=';
                        }
                } else {
                        *dst++ = encode_bits(((a & 3) << 4));
                        *dst++ = '=';
                        *dst++ = '=';
                }
                olen += 4;
                line += 4;
                if (line == 64) {
                        line = 0;
                        *(dst++) = '\n';
                        olen++;
                }
        }
        return olen;
}

int ceph_unarmor(char *dst, const char *src, const char *end)
{
        int olen = 0;

        while (src < end) {
                int a, b, c, d;

                if (src[0] == '\n') {
                        src++;
                        continue;
                }
                if (src + 4 > end)
                        return -EINVAL;
                a = decode_bits(src[0]);
                b = decode_bits(src[1]);
                c = decode_bits(src[2]);
                d = decode_bits(src[3]);
                if (a < 0 || b < 0 || c < 0 || d < 0)
                        return -EINVAL;

                *dst++ = (a << 2) | (b >> 4);
                if (src[2] == '=')
                        return olen + 1;
                *dst++ = ((b & 15) << 4) | (c >> 2);
                if (src[3] == '=')
                        return olen + 2;
                *dst++ = ((c & 3) << 6) | d;
                olen += 3;
                src += 4;
        }
        return olen;
}